Effects of Frame Design and Cab Suspension on the Ride Quality of Heavy Trucks

Abstract

Frame and cab suspension designs of Class 8 heavy trucks were investigated to see their effects on ride comfort. Four trucks were used in this study, each with a different frame: a factory low frame, a lightweight low frame, a factory high frame, and a lightweight high frame. There were two different frame heights and three thicknesses. Two different rear cab suspensions were also tried out on each truck. Both suspensions used two airsprings and two dampers mounted vertically to control the vertical motion. The first suspension used two horizontally mounted dampers to control the lateral motion, while the second used a panhard rod connected to a torsion spring. In addition, two different sets of airsprings and two sets of vertical shocks were tried with each suspension, giving eight suspension combinations. The trucks were shaken through the forward drive (second) axle using two 5500 lb hydraulic actuators with displacement control. The steering (first) axle was left in contact with the ground (through the tires) and the rear drive (third) axle was strapped to the truck's frame and acted solely as dead weight. The actuators were given various inputs including single frequency sinusoidal signals, step signals, and decreasing amplitude chirp signals. Both roll and heave modes of the truck were excited. The ride was measured using three accelerometers located at the B-post inside the truck cab. These accelerometers were oriented in the vertical, fore/aft (longitudinal), and lateral (left/right) directions. Numerous other accelerometers and LVDTs were used to measure frame and cab motion. This study found that there while the beaming frequency shifted downward with the lighter frames, there was only a small decrease in ride quality. The panhard suspension rod had significantly higher roll motion, but the heave amplitudes were similar to the lateral damper suspension. Switching vertical shocks had a significant effect on heave motion, but none on the cab's roll. Switching the airsprings on the cab suspension in this study had no effect.